Slow headgasket failure? Would you bother to fix?

I am betting I have a slow headgasket leak that might be getting worse.
The truck has always blown bubbles in the puke tank after shut down. No oil in the water, no water in the oil (that I could see), no significant coolant consumption. This has gone on for eight years and about 50k miles. Hasn't gotten any worse. I always figured it was a lower intake leak, maybe the headgasket. About three years ago it started fouling plug #5 and throwing a misfire code. I had the compression checked at the time and the numbers were good. I have since replaced that plug about four or five times. It will foul that plug and only that plug every few thousand miles. Is the replacement interval getting shorter? Maybe. I haven't kept track of the dates. Now on really cold mornings (we have had a cold winter this year) I smell a little coolant on startup and she rattles a bit near that #5 cylinder for a few seconds then quiets down (it's done the rattle for years). I am about to change that plug again for the 5th or 6th time and I am starting to wonder if this is finally catching up with me.
What would you do in my place? Replace just one gasket? Both? Rebuilt heads? Crate motor? Spend the cash on a new truck? It's a great truck otherwise but it's hardly in showroom condition. It needs ball joints and tie rods, paint is going on the roof and hood. Everything else is in pretty good shape. It's my daily driver but I only drive about 6k miles a year. I think there is 225k on the clock, 50-60k on the trans. 4x4 works great, tires are good. I am hoping to get another 6-12 months out of it. Wife gets a car this year. Suggestions welcome.

If you can do the work yourself, do the gaskets. Have the heads checked for cracks if you don't see any signs of apparent gasket leakage. Better to schedule the downtime than let the engine schedule it for you.

If you have the heads off, disassemble them and have them magnafluxed and checked for cracks. Vortec heads are really bad about cracking, and it can be hard to spot the cracks.

SAATR said:

If you can do the work yourself, do the gaskets. Have the heads checked for cracks if you don't see any signs of apparent gasket leakage. Better to schedule the downtime than let the engine schedule it for you.

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That’s what I did on my son’s 98. Hydrolocked on #5 with coolant in the oil. I pulled the head expecting a gasket break. The head was cracked instead and the other one was as well. I put a set of reman heads on it, total cost for everything was probably just shy of $1,000.

We got nearly a year out of it before it started knocking a few weeks ago.

It’s a tough call. Hope for a gasket but budget for something worse just in case.

I hadn't considered a cracked head. I'm wondering if it's worth a teardown and the cost of rebuilt heads on a 1/4 million mile engine.
Yeah, I can probably do the work myself. I have already done the lower intake twice. I haven't done heads in 30 years but I can figure it out. Biggest issue for me is time and space.

tinfoil_hat said:

I am betting I have a slow headgasket leak that might be getting worse.
The truck has always blown bubbles in the puke tank after shut down.

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Entirely common--normal, actually--for the coolant temp to increase after shutdown. The hot iron is still transfering heat to the coolant, but the coolant is no longer circulating.

If the coolant is near-boiling when shut down, it could be boiling afterwards. But it wouldn't have to be boiling, just hot enough to increase pressure, which then relieves via the rad cap. It would appear to be "blowing bubbles" in the overflow tank.

FIRST things to do is to check anti-freeze concentration, engine normal operating temp, and the temp increase after shutdown.

tinfoil_hat said:

No oil in the water, no water in the oil (that I could see), no significant coolant consumption. This has gone on for eight years and about 50k miles. Hasn't gotten any worse. I always figured it was a lower intake leak, maybe the headgasket.

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No "significant" coolant consumption in eight years and not getting worse, would counter-indicate a failed gasket or cracked casting.

tinfoil_hat said:

About three years ago it started fouling plug #5 and throwing a misfire code. I had the compression checked at the time and the numbers were good. I have since replaced that plug about four or five times. It will foul that plug and only that plug every few thousand miles. Is the replacement interval getting shorter? Maybe. I haven't kept track of the dates. Now on really cold mornings (we have had a cold winter this year) I smell a little coolant on startup and she rattles a bit near that #5 cylinder for a few seconds then quiets down (it's done the rattle for years). I am about to change that plug again for the 5th or 6th time and I am starting to wonder if this is finally catching up with me.

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#5 plug is fouling HOW? Oil fouled? Fuel fouled? Coolant fouled?

In general, coolant doesn't so much "foul" a plug as it steam-cleans the plug and the whole combustion chamber. If you had enough coolant getting on the plug to foul it, you'd notice coolant loss.

Rattling near #5 and coolant loss could indicate enough coolant in the cylinder to create pressure spikes if not outright hydrolocking. But if it hydrolocked, you wouldn't have good compression numbers, and if there were that much coolant in the chamber...your radiator would be low on fluid.

Another possibility: "rattling" when cold is typical GM piston slap that goes away when warm. GM claims that piston slap is "harmless", but that's because if they admitted it was a problem, they'd be obligated to repair all the piston-slapping engines that were still under warranty when the slapping started--and that's tens of thousands of engines--maybe millions--over the years.

tinfoil_hat said:

What would you do in my place? Replace just one gasket? Both? Rebuilt heads? Crate motor? Spend the cash on a new truck?

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"I" would pop out the spark plugs out of a fully-cold engine, disconnect power from the ignition coil. Pump the cooling system up with a pressure tester, leave it overnight. Next morning, check the pressure, then have someone turn the key to "Crank" and see if coolant shoots out of a spark plug hole or two. This is not a guaranteed diagnosis--sometimes gaskets or cracked castings only leak under combustion pressure of hundreds of PSI, not under the sixteen psi of a radiator pressure tester. Sometimes they only leak when hot. But it's a start.

I certainly would not panic and buy a new truck, or even a new engine. But then, I'm known for putting ball-joints and fuel pumps and even engines into rusty old crap other folks would tow to the Treasure Yard.

Let's do some diagnosis first, before spending real money.

Well, that's an interesting take. I will pull the plug in the morning and post a picture. My theory had been that a little seepage was happening as the truck cooled off, then sealed as it heated up and everything swelled tight.

@tinfoil_hat What year is your engine?

So you've known or suspected a condition that could go catastrophic anytime. You said it passed a compression check? What kind? Total pressure or cylinder leak down? All passed with what? Was there more than 20% variation? What year, upgraded injection or stock poopoot ? Fouled plug by what carbon, fuel, oil, shop rag?
And yes the morons working on an opposed air-cooled six cylinder left a shop rag in cylinder then tried to install it.
I saw and watched the " must have direct supervision team" struggling. " Did you look in spark plug hole?" A very quiet....no. " WELL?" Ah it's red and .,..fuzz....
Everybody is watching you could a pin drop. The rest of afternoon we had training practice, practice, practice, practice.
Practice makes perfect.

Man one time i dropped the trans pan on a Escalade i had for a filter change and whoever was there before left a red shop rag in it.